Electronic tube alarm circuit



Oct. 23, 1956 K. I UToMlRsKl 2,768,291

ELECTRONIC TUBE ALARM CIRCUIT Filed April 2l. 1952 II'HI i I Q93 '1 'i |I E 'c i Q I S vWww-[llllllllr-{rl /NVEA/TOR K. UroM/Rsk/ 5 ATTORNEY ELECTRONIC TUBE ALARM CIRCUIT Karel Lutomirski, Brooklyn, N. Y., assigner to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application April 21, 1952, Serial No. 283,499

3 Claims. (Cl. Z50-27) This invention relates to electronic devices and particularly to alarm means for indicating deterioration of continuously operating tubes such as amplifiers, rectifiers and oscillators.

Objects of the invention are the prevention of failure of continuously operating electronic devices such as ampliers, rectifiers and oscillators and to this end the provision of alarm means for indicating deterioration sufficient to justify replacement of a device prior to failure.

It is known to provide alarm means operative upon failure of an electronic tube for anyone of various reasons such as a burned out filament or failure of a voltage source; and it is known to provide a relay which releases responsive to such a failure to close an alarm circuit. However, such alarm means lacks the capability of giving a warning of deterioration in advance of failure because there is a wide variation in the level to which the energizing current must be reduced to effect release.

This invention is a deterioration determining arrangement for continuously operating electronic devices comprising a differential relay having one Winding included in an output circuit of an electronic device employed in continuously s-upplying an output current of desired value and a biasing winding energized to prevent operation a-s long as the desired output current is maintained within certain limits. The relay operates to close an alarm circuit as soon as the current in the output circuit which includes the one winding either increases or decreases an amount suiiicient to indicate a trouble condition or deterioration to a point justifying replacement of the device before it fails entirely. It is further to be observed that this alarm `arrangement is also operative when applied to an electronic tube in case of complete tube failure, in case the anode potential supply fails and also in case the voltage supply for the biasing winding fails.

A clear and complete understanding of the invention will be facilitated by descrip-tion of one embodiment as shown schematically in the drawing. The invention is, however, not limited in its application to the arrangement disclosed in the draw-ing but is generally applicable to electronic devices employed in producing a continuous direct current output within certain limits of amplitude.

The drawing, which consists of a single figure, shows an electronic tube oscillator of the bridge-stabilized type for supplying current of a desired frequency within the voice band, together with alarm apparatus for giving an alarm not only in the case of tube failure but also whenever deterioration of the tube sutiicient to justify tube replacement is indicated by a reduction of the output current below a predetermined value. This oscillator circuit, which is similar to that shown and described in detail both as to structure and theory of operation in Patent 2,303,485 granted to L. A. Meacham, December 1, 1942, comprises an electronic tube 10, a retard coil 21, a varistor 25, an output transformer 30, alarm relays 36 and 40 and a number of condensers and resistors hereinafter identified, The tube is a pentode having an indirectly heated cathode, the heater element being shown but not the source of nited States Patent O current for heating this element. The anode-cathode circuit of tube is traced from the anode through the winding 31 of transformer 30, resistor 17, fuse 18, battery 19, ground, battery 39, fuse 37, upper winding of alarm relay 36 and resistor 11 to the cathode. The frequency and amplitude of the current are controlled by the bridge circuit in which windings 31 and 32 constitu-te adjacent arms, -a third arm consists of resistors 33 and 34 and condenser 26, and the fourth arm is the antiresonant network consisting of condenser 20, retard coil 21, condensers 22 and 23 and varistor 25 which is connected to shunt a desired part of the retard coil winding. The antiresonant network is tuned to the desired oscillation frequency, some adjustment of frequency being provided by v-ariable condenser 23. Variable resistor 34 enables adjustment of the output voltage. Blocking condensers 16, 20 and 26 isolate the anode battery 19 from the antiresonant network and grid of the tube. The grid-cathode circuit includes resistors 12, 13 and 11, and resistor 14 supplies positive potential from battery 19 to the screen grid. The varistor 25 makes the impedance of the antiresonant network vary with voltage amplitude having a high effective resistance which decreases rapidly as the voltage increases. For frequencies above or below the antiresonant frequency to which the network is tuned, the network is respectively a capacitative or inductive reactance of a magnitude which decreases as the frequency departs further from antiresonance. The eiect of frequency variation on the phase angle of the impedance near antiresonance and the effect of voltage amplitude variation on the magnitude of the antiresonant impedance are such as to stabilize the frequency and amplitude of the oscillations.

The differential alarm relay 36 is biased by energization of its lower winding so that normal anode-cathode current through the upper winding is ineective to operate this relay. If and when the internal impedance of the tube increases sufficiently to indicate that the tube should be replaced although the output is Within allowable limits, the decrease in energization of the upper winding of relay 36 results in operation of the relay by its biasing, lower winding. Furthermore, if and when the anode-cathode current increases beyond a normal maximum level due to some trouble condition, for instance a trouble ground on the grid or an open varisltor 25, the increase in the energization of the upper winding causes the operation of relay 36. The operation of relay 36 closes a circuit for operating relay 40; and the operation of relay 40 closes circuits for lighting alarm lamp 41 and for operating an audible alarm 42. The tube may then be replaced prior to further deviation or failure of the output voltage. lt should be noted that upon oper-ation of either of fuses 18 or 37 in the anode-cathode circuit or any other failure of the anode-cathode circuit voltage supply, the alarm relay operates. Further, in case the fuse 38 in the biasing circuit of relay 36, the continued operation of the oscillator causes operation of the al-arm relay by its upper winding thus to operate the alarms indicating the need of maintenance attention.

The alarm relay when oper-ated may cause transfer from the device with which the relay is associated to a standby device so that there is no interruption of the voltage sup ply while the defective device is being replaced.

What is claimed is:

1. In combination, an oscillator unit comprising an electronic tube, tube energizing means, a load element connected in the anode-cathode circuit of said tube, an alarm control relay, alarm means energized by operation of said relay, said relay comprising differential windings, one winding connected in series with said load element in the anode-cathode circuit of said tube, and means comprising a portion of said tube energizing means for ener gizing the other winding of said relay to cause operation of the relay when current in said one Winding falls to a value indicating tube deterioration sufficient `to justify tube replacement. Y

2. In an oscillator unit comprising an electronic tube, tube energizing means, a load element connected in the anode-cathode circuit of said tube, an alarm control relay, alarm means energized by operation of said relay, said relay comprising diierential windings, one Winding connected in series with said load element in the anode-cathode circuit of said tube, and means comprising a portion of said tube energizing means for energizing the other Winding of said relay for biasing the relay to prevent operation when the current in said circuit is within predetermined limits, an increase in the anode-cathode current beyond a certain value being effective to operate said relay.

3. In a circuit arrangement comprising an electronic tube, tube energizing means, a load element connected in the output circuit of said tube, an alarm control relay, alarm means energized by operation of said relay, said relay comprising differential windings, one Winding connected in said output circuit of said tube, and means coruprising a portion of said tube energizing means for energiz-ing the other Winding of said relay to a degree which prevents operation of the relay While the current in said circuit is Within predetermined limits, a change in the amplitude of the current through said one winding beyond said limits being effective to operate said relay.

References Cited in the le of this patent UNITED STATES PATENTS 1,462,057 Wold July 17, 1923 1,503,709 Pruden Aug. 5, 1924 1,690,271 Clement Nov. 6, 1928 1,711,663 Van Der Bijl May 7, 1929 2,261,153 Gieringer Nov. 4, 1941 2,326,313 Trucksess Aug. 10, 1943 FOREIGN PATENTS 355,666 Great Britain Aug. 2l, 1921 

